1. Field of the Invention
The present invention relates to a secondary battery and, more particularly, to a secondary battery with an electrode assembly fixing device that can prevent deformation and variation in volume of the electrode assembly during charging and discharging operations.
2. Description of the Prior Art
Generally, secondary batteries are compact in size and rechargeable, while providing a large capacity. Well known as secondary batteries are a lithium-ion battery and a lithium-ion polymer battery.
The lithium-ion battery uses lithium metal oxide as a positive active material and carbon or a carbon compound as a negative active material. Lithium salt dissolved in an organic solvent is used as an electrolyte via which lithium ions move between positive and negative electrodes.
In addition, the lithium-ion polymer battery uses a hybrid polymer as separators disposed between the positive and negative electrodes. The electrolyte is impregnated into the separators made of the hybrid polymer so that charging and discharging operations are realized while the lithium ions are moved between the positive and negative electrodes via the separators.
FIG. 5 shows a conventional prism-type lithium-ion battery.
A rolled electrode assembly 2 is inserted into a can 4 filled with electrolyte, the rolled electrode assembly 2 comprising positive and negative electrodes and separators disposed between the positive and negative electrodes. Mounted on an upper end of the can 4 is a cap assembly 6.
In the conventional lithium-ion battery structured as in the above, the can 4 has to be designed having sufficient strength to withstand pressure generated when the rolled electrode assembly 2 repeatedly expands and contracts as the battery is charged and discharged. For example, when the can 4 is made of iron or aluminum, the can 4 is designed to have a thickness of about 0.4-0.6 mm, making it difficult to reduce the weight of the battery. That is, the weight of the iron can is about 17 g, and the weight of the aluminum can is about 8-9 g.
In addition, the expansion and contraction of the rolled electrode assembly 2 causes active material to be removed therefrom, deteriorating reliability of the battery. Furthermore, it is easy for the rolled electrode assembly 2 to be deformed when it receives external impact, thereby degrading the battery.